如何向每个面添加水平平均线和注释

Question

我有一个 2 行 1 列的简单 FacetGrid，其中的线图表示构面的不同类别 - 如下图。

# lineplot for each Category over the last three years
g = sns.FacetGrid(df, row="Category", sharey=False, sharex=False, height=2.5, aspect = 3)
g = g.map(plt.plot, 'Date', 'Count')

如何添加显示每个方面的平均计数的参考线和注释？

样本数据

• 读取示例数据框

# lineplot for each Category over the last three years
g = sns.FacetGrid(df, row="Category", sharey=False, sharex=False, height=2.5, aspect = 3)
g = g.map(plt.plot, 'Date', 'Count')

df.head()

import pandas as pd

data = {'Category': ['Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1', 'Group 1',
                     'Group 1', 'Group 1', 'Group 1', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2',
                     'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2', 'Group 2'],
        'Date': ['2017-01-31', '2017-02-28', '2017-03-31', '2017-04-30', '2017-05-31', '2017-06-30', '2017-07-31', '2017-08-31', '2017-09-30', '2017-10-31', '2017-11-30', '2017-12-31', '2018-01-31', '2018-02-28', '2018-03-31', '2018-04-30', '2018-05-31', '2018-06-30', '2018-07-31', '2018-08-31', '2018-09-30', '2018-10-31', '2018-11-30', '2018-12-31',
                 '2019-01-31', '2019-02-28', '2019-03-31', '2019-04-30', '2019-05-31', '2019-06-30', '2019-07-31', '2019-08-31', '2019-09-30', '2017-01-31', '2017-02-28', '2017-03-31', '2017-04-30', '2017-05-31', '2017-06-30', '2017-07-31', '2017-08-31', '2017-09-30', '2017-10-31', '2017-11-30', '2017-12-31', '2018-01-31', '2018-02-28', '2018-03-31',
                 '2018-04-30', '2018-05-31', '2018-06-30', '2018-07-31', '2018-08-31', '2018-09-30', '2018-10-31', '2018-11-30', '2018-12-31', '2019-01-31', '2019-02-28', '2019-03-31', '2019-04-30', '2019-05-31', '2019-06-30', '2019-07-31', '2019-08-31', '2019-09-30'],
        'Count': [226, 235, 236, 221, 187, 218, 225, 221, 248, 224, 204, 224, 218, 241, 196, 246, 256, 217, 229, 230, 222, 215, 226, 227, 232, 233, 224, 214, 243, 214, 235, 218, 208, 208, 254, 223, 227, 245, 222, 226, 235, 225, 226, 258, 234, 257, 224, 228, 222, 227, 256, 217, 243, 230, 250, 197, 232, 248, 232, 259, 259, 229, 228, 234, 218, 231]}

df = pd.DataFrame(data)
df.Date = pd.to_datetime(df.Date)

Answer 1

• 根据中的警告seaborn.FacetGrid，最好使用图形级函数，例如sns.relplot.

g = sns.relplot(data=df, kind='line', x='Date', y='Count', row='Category', height=2.5, aspect=3, facet_kws={'sharey': True, 'sharex': False})
g.fig.tight_layout()


def custom(y, **kwargs):
    ym = y.mean()
    plt.axhline(ym, color="orange", linestyle="dashed")
    plt.annotate(f"mean: {y.mean():.3f}", xy=(1,ym), 
                 xycoords=plt.gca().get_yaxis_transform(), ha="right")
    

g = g.map(custom, 'Count')

只需一行就足够了

g = sns.FacetGrid(df, row="Category", sharey=False, sharex=False, height=2.5, aspect = 3)
g = g.map(plt.plot, 'Date', 'Count')

# add this to get a horizontal line
g = g.map(lambda y, **kw: plt.axhline(y.mean(), color="k"), 'Count')

要使线条橙色和虚线并添加注释，您可以这样做

def custom(y, **kwargs):
    ym = y.mean()
    plt.axhline(ym, color="orange", linestyle="dashed")
    plt.annotate(f"mean: {y.mean():.3f}", xy=(1,ym), 
                 xycoords=plt.gca().get_yaxis_transform(), ha="right")
    

g = sns.FacetGrid(df, row="Category", sharey=False, sharex=False, height=2.5, aspect = 3)
g = g.map(plt.plot, 'Date', 'Count')
    
g = g.map(custom, 'Count')